Field of the Invention
This disclosure relates to a power switch and, more particularly to a power switch used in an electronic device.
Description of the Related Art
A DC-DC switching power supply is commonly used in an electronic device to provide power to load circuits in the electronic device. The DC-DC switching power supply includes various power switches such as a metal oxide semiconductor field effect transistor (MOSFET) cell. The various power switches have different features and are suitable for different situations.
For example, the power switch with larger channel area usually has lower conducting resistance and loss of conduction, the power switch is suitable for heavy loads. However, larger channel area of power switch simultaneously has higher gate capacitance Qg which generates high driving loss in operation.
When the DC-DC switching power supply drives a light load, the conducting loss is low, and the driving loss becomes more significant. Thus the power switch of high gate capacitance makes the DC-DC switching power supply have poor efficiency in light load due to the loss of the gate capacitor.
Furthermore, the power switch with the lower channel area usually has larger conducting resistance RDS(ON) which generates high conducting loss and is unsuitable for driving the heavy load. Contrarily, the power switch of smaller channel area has lower gate capacitance Qg and thus the driving loss is low. While operating in the light load, the conducting loss is low and the driving loss is relative important. Thus the power switch of lower gate capacitance has better efficiency.